A total occlusion is present when there is no flow of blood through the artery due to a blockage. An acute total occlusion is usually considered to be an occlusion that has occurred within the past 7 days, especially as the result of a myocardial infarction. A chronic total occlusion is an occlusion that is no longer acute and can be several months or years old. Successful revascularization improves angina status, increases exercise capacity, and reduces the need for late bypass surgery.
The patients of chronic total occlusion frequently present with a change in angina status rather than acute myocardial infarction. Well-developed collaterals may provide flow equivalent to a 90-95% stenosis, which helps maintain myocardial viability and prevents resting myocardial ischemia. Pathologically, the major constituent of a chronic total occlusion is fibrocalcific plaque. These obstructions are often resistant to guidewire crossing, accounting for lower success rate compared to nontotal occlusion.
Compared to PTCA (percutaneous transluminal coronary angioplasty) of nontotal occlusion, revascularization rates for chronic total occlusion remain disappointingly low. The most common reasons for procedural failure include the inability to cross the occlusion with a guidewire, failure to cross the occlusion with a balloon, and failure to dilate the stenosis. Recently, use of the rotablator catheter has decreased procedural failure due to lesion rigidity.
Jenkins in U.S. Pat. No. 5,109,859, entire contents of which are incorporated herein by reference, discloses an ablative laser element aiming at the plaque to ablatively remove the plaque under computer guidance. In one embodiment, the laser is able to fire in a forward direction after first determining the laser's path to be intralumnal in order to create or recanalize a central channel. In another embodiment, the laser is able to fire circumferentially at the arterial wall guided as to depth and direction by the ultrasound computer interface.
Loeb et al. in U.S. Pat. No. 6,845,193, entire contents of which are incorporated herein by reference, discloses a laser device for forming a channel through an occlusion or plaque in a blood vessel. The device comprises a fiber optic conduit which is adapted to be coupled to a source of laser energy, a hollow sheath which covers distal end of the fiber optic conduit and defines a pocket, and a fiber optic lens in the pocket and adapted to receive and direct the laser energy emitted from the fiber optic conduit through the lens onto the occlusion and to form a channel therethrough.
Vulnerable plaques are atherosclerotic plaques associated with erosion and ulceration that prone to rupture leading to acute embolization and thrombus. Until recently, physicians believed that most heart attacks were caused by a gradual buildup of atherosclerotic plaque in the arteries of the heart that eventually impeded blood flow. In fact, up to half of all sudden, out-of-hospital cardiac deaths occur in people with no prior diagnosis of heart disease and over two-thirds of heart attack suffers have blockages in their arteries considered to be clinically insignificant in terms of plaque burden and percent stenosis.
Most ruptured plaques are characterized by a large lipid pool and a thin fibrous cap with macrophage infiltration. On the other hand, calcified plaque deposits typically comprise hard material that restricts blood flow in a blood vessel. But, atherosclerotic plaque may also comprise combinations of soft and hard materials. The main difference between a soft vulnerable plaque and a hard stable plaque lies in the risk for a vulnerable plaque to rupture suddenly. The risk of plaque rupture is greatest when the fibrous cap is very thin or the plaque lipid pool is very large.
The buildup of plaque in the blood vessels is sometimes referred to as atherosclerosis, or hardening of the arteries. Atherosclerosis often begins as a small injury to an artery wall. This injury triggers a cascade of injury and response, inflammation, and healing, which may ultimately lead to the narrowing of the artery. It is generally believed that inflammation in an arterial plaque is the result of a series of biochemical and mechanical changes in the arterial wall. The inflammatory cells collect the debris of the damaged tissue resulting in a core of lipid, including macrophages or foam cells and necrotic tissue that is covered by a thin fibrous cap of scar tissue. If the fibrous cap becomes weakened, eroded, or is subjected to excessive mechanical stress, it may rupture and expose the thrombogenic damaged endothelium and metabolic byproducts to the blood stream that causes blood clotting. If the resulting blood clot is severe enough, it may occlude the artery. If this obstruction persists in a coronary artery, a myocardial infarction or angina may result.
Many vulnerable plaque deposits do not obstruct the flow of blood through the blood vessels. Vulnerable plaques are often undetectable using conventional techniques such as angiography. However, a plaque may rupture suddenly and form a blood clot in the blood vessel lumen causing a blockage and causes heart attack and death. Recently, inflammation has been recognized being associated with the formation and progression of vulnerable plaques. An increase in tissue temperature at a lesion is thought to be caused by the response of the immune system to inflammation and an increase in metabolic activity involved in the healing process. It has been observed that the inflamed necrotic core of a vulnerable plaque maintains itself at a temperature which may be a fraction of a degree to a few degrees higher than the surrounding tissue. Vulnerable plaques are generally characterized by hemodynamically insignificant, variable in size, not calcified, and undetectable with standard anatomic imaging methods.
The inability of common diagnostic methodologies, such as coronary angiography that is the current gold standard technique for diagnosing coronary vessel obstructions, to detect vulnerable plaque has led to a major rush to develop new methods to detect, characterize and treat patients with these types of deposits. Unlike the typical occlusive atherosclerotic lesion, vulnerable plaque deposits are associated with a compensatory enlargement of the vessel wall known as positive lumen remodeling. Selected intravascular imaging techniques for vulnerable plaque include angioscopy, intravascular ultrasound, thermography, optical coherence tomography, elastography, magnetic resonance imaging, nuclear imaging, electrical impedance imaging, shear stress imaging, photonic spectroscopy, and the like. Among them, catheter-based intravascular thermography is the most promising one, which is based on the premise that vulnerable plaques are hotter than surrounding normal tissue and that by measuring these temperature elevation, physicians can determine the exact location and extent of disease.
Casscells and associates (Current Opinion in Cardiology 2002; 17:656-662) reported mechanism of heat production in atherosclerotic plaques by a high metabolic rate in the areas of macrophage accumulation, of which a sub-population strongly expresses mitochondrial uncoupling proteins. The uncoupling proteins are homologs of thermogenin, which is responsible for thermogenesis in brown fat tissue. Further, they measured temperature of living samples with a thermistor and found that plaques showed several regions in which the surface temperatures varied reproducibly by 0.2° C. to 0.3° C. Infrared thermographic images also revealed heterogeneity in temperature among the plaques.
U.S. Pat. No. 5,924,997 to Campbell, entire contents of which are incorporated herein by reference, discloses an intravascular catheter system capable of mapping thermal variations in the temperature of atherosclerotic plaque by a plurality of thermal sensors fixedly attached along the catheter. The thermal sensors are mounted on the catheter shaft and soldered to a conductor while each sensor needs a conductor. The spacing of the mechanical thermal sensors arrangement allows only limited sensors to be placed within a unit length.
U.S. Pat. No. 6,292,695 to Webster, Jr. et al., entire contents of which are incorporated herein by reference, discloses a basket shaped catheter with a plurality of electrodes on each expandable member of the basket, while each electrode may comprise a thermal sensor for temperature monitoring. The spacing of the electrodes with mechanical thermal sensors arrangement allows only limited sensors to be placed within a unit length on each expandable member of the basket.
U.S. Pat. No. 6,450,971 to Andrus et al., entire contents of which are incorporated herein by reference, discloses a balloon catheter having temperature responsive material designed to exhibit at least one predetermined color when the material is in contact with an object having an elevated temperature, wherein a light detector positioned to indirectly detect the color change indicative of suspected lesion. The Andrus et al. balloon catheter uses a moving light detector to map multiple lesion sites within a blood vessel.
U.S. Pat. No. 6,475,159 to Casscells et al, entire contents of which are incorporated herein by reference, discloses an infrared heat-sensing catheter using an infrared fiberoptic system at the tip of the catheter to locate a single inflamed, heat-producing atherosclerotic plaque. The Casscells et al. catheter uses a dragging method to map multiple lesion sites within a blood vessel.
U.S. Pat. No. 6,514,214 to Kokate et al., entire contents of which are incorporated herein by reference, discloses a catheter with at least one temperature sensor disposed proximate to the distal end of the elongate shaft adapted to contact an inner surface of the blood vessel. The Kokate et al. catheter uses a dragging method to map multiple lesion sites within a blood vessel.
None of the above-identified patents discloses a thermal sensing means for measuring a plurality of contiguous points without dragging the device for area thermal mapping. In a co-pending patent application Ser. No. 10/373,539, filed Feb. 24, 2003, there is disclosed an optical thermal mapping device and methods for monitoring the thermal profiles enabling detecting vulnerable plaques within a blood vessel on a real time basis. The thermal mapping of vulnerable plaques using at least one optic fiber with multiple optical gratings are disclosed therein without dragging the device for area thermal mapping. Further in a co-pending patent application Ser. No. 10/877,867, filed Jun. 26, 2004, there is disclosed an optical thermal mapping device comprising multiple optic fibers with optical gratings for monitoring the thermal distribution of, and detecting and photodynamically treating vulnerable plaques within blood vessels.
Optic fibers are hair thin strands of glass or plastic that guide light. The optic fiber has an inner core surrounded by an outer cladding. In order to guide light, the core refractive index is higher than the cladding index. A fiber grating, which the periodic structure of the refractive index is formed inside the core of a fiber, is widely used in the field of fiber-optic communication for wavelength management. The optical grating reflects or transmits a certain portion, wavelength (bandwidth) or intensity, of the light along optic fibers. A fiber Bragg grating is based on the interference of multiple reflection of a light beam in a fiber segment whose index of refraction varies periodically along the length of the fiber. Variations of the refractive index constitute discontinuities that emulate a Bragg structure. If the spacing of the index periods is equal to one half of the wavelength of the light, then the waves will interfere constructively (the round trip of each reflected wave is one wavelength) and a large reflection will occur from the periodic array. Optical signals whose wavelengths are not equal to one half the spacing will travel through the periodic array unaffected.
A periodic variation of the refractive index is formed by exposing the core, such as germanosilicate, of the fiber to an intense ultraviolet (UV) optical interference pattern or mask that has a periodicity equal to the periodicity of the grating to be formed. When the fiber is exposed to an intensive UV pattern, structural defects are formed and thus a permanent variation of the refractive indexes having the same periodicity with the UV pattern. The condition for strong reflection of Bragg wavelength is λ=2×n×d. Where n is the effective refractive index, and d is Bragg spacing or grating period. Both n and d change with changes in temperature due to thermal-optic and thermal expansion effects.
The merits of optic fiber sensors include immunity to electromagnetic interference, high flexibility, remote sensing capability, smaller size of sensing element, lightweight, little thermal/electric conductivity, and easy to fabricate. Optic fiber sensors have been developed for chemical, strain, temperature and pressure sensing, and smart structure inspection. Various fiber-grating configurations have been developed for sensor application. Depending on its configuration, in general, it can be classified as direct and indirect sensors. Direct sensors measure the environmental effects surrounding the grating. Indirect sensors measure the environmental effects at the tip of the fiber and use fiber grating for wavelength management. The sensing signal is obtained through either a transmission or reflection mode. In some aspect of the present invention, it is provided direct fiber grating as direct sensors in a reflection mode.
Fiber gratings reflect light of particular bandwidth, and can act as high-performance optical thermal sensor. The reflected bandwidths are extremely narrow because of the long path lengths possible in optic fibers. Therefore, a minute temperature change surrounding the fibers changes the effective refractive index and grating's periods, thus modulating their reflective wavelength or intensity. When multiple gratings are created in an optic fiber, a multi-point sensor can be monitored simultaneously.
Fiber-grating technologies have been proven and demonstrated with excellent sensing abilities for temperature, pressure, stress and various chemicals detection. They also exhibit extremely long-term stability, and minimal optical losses. Several prior art devices have been described for the performance of a number of optic fiber grating sensors. U.S. Pat. No. 5,627,927 discloses an interferometer fiber grating for sensing the environmental effect at the termination of the fiber. U.S. Pat. No. 6,072,922 discloses a cryogenic fiber optical sensor by introducing additional thermal strain in the fiber to enhance sensor sensitivity. U.S. Pat. No. 5,444,803 discloses a fiber-optic device including fiber grating and mode stripper to admit only one mode for sensor application. U.S. Pat. No. 6,018,160 discloses an apparatus using two optical gratings for sensing aircraft skin temperature and/or strain. The above-referred patents, U.S. Pat. Nos. 5,627,927, 6,072,922 5,444,803, and 6,018,160, entire contents of all being incorporated herein by reference, disclose fiber-grating technology suitably applicable in the present invention for monitoring the thermal distribution of, and detecting vulnerable plaques within a blood vessel.
U.S. Pat. No. 6,753,160 to Adair, entire contents of which are incorporated herein by reference, discloses a method for diagnosis and treatment of arteriosclerotic lesions wherein the method is characterized by introducing a chemical compound to the patient, the compound being a complex of a photosensitive portion and a radioactive portion. Cells which exhibit an affinity for the porphyrin element indicate sites of plaque buildup. The radioactive portion within the compound allows tomographic scanning as well as simultaneous radiation treatment. The complexed compound can be introduced to the patient a desired number of times to provide the necessary radiation treatment and ongoing monitoring of plaque removal.
U.S. Pat. No. 6,736,808 to Motamedi et al., entire contents of which are incorporated herein by reference, discloses a catheter capable of both sensing myocardial electrical activity and delivering ablating energy within myocardial tissue, wherein the catheter may have a stabilizer of disk or basket shaped extensions which are attached to the catheter's distal tip. The catheter further comprises electrodes on the outer sheath and contains a movable fiber optic cable that can be percutaneously advanced beyond the catheter body and into the myocardium for myocardial heating and coagulation.
Robinson et al. in U.S. Pat. No. 6,054,449 and No. 6,794,505, entire contents of which are incorporated herein by reference, discloses a broad class of photosensitive compounds having enhanced in vivo target tissue selectivity and versatility in photodynamic therapy. reactive oxygen or chlorin producing photosensitizers are photoactivatable compounds having an affinity for hyperproliferating cells, which when photoactivated, produce cytotoxic reaction products. Some aspects of the present invention relative to a method for treating vulnerable plaque tissue in a blood vessel comprising providing an elongate tubular catheter into intimately contacting the tissue with a plurality of expandable basket optic fibers, each fiber having at least one optical grating facing the tissue-contacting surface alone for measuring the plaque tissue temperature and treating the tissue photodynamically with reactive oxygen and/or chlorin products.
U.S. Pat. Application publication 2004/0092830 and U.S. Pat. Application publication 2004/0093044, entire contents of both are incorporated herein by reference, disclose light delivery catheters for treatment of diseased vessels. Some optic fiber lumen is provided in the catheter shaft for containing a treatment optic fiber for delivering treatment light from a light source at the proximal end of the catheter shaft to the light transmission zone. The light intensity and efficiency is greatly compromised by the obstructive blood flow, including blood cells, platelets, plasma, and other electrolytes in photodynamically treating the lesion. Some aspects of the present invention provides an elongate tubular catheter at about the target tissue region, wherein the catheter comprises at least one optic fiber having at least one optical grating along an axis of the fiber, wherein the fiber further comprises a light transmission zone intimately contacting the tissue region configured for photodynamic therapy
Although many prior art patents are related to percutaneous transluminal coronary angioplasty, none of them discloses an optical medical device system having laser-induced micro pressure wave capability for crossing and breaking-up chronic total or near-total occlusion.